The charge and discharge curve is a very important part of the lithium battery's electrical performance parameters, because it can reflect the true application voltage platform and internal performance of the lithium battery.

　　As we all know, the charge-discharge curve of lithium cobalt oxide battery is relatively steep, and the charge-discharge voltage curve of lithium iron phosphate battery is relatively straight.

　　The picture below is a comparison of the charge and discharge curves of a lithium cobalt oxide battery and a lithium iron phosphate battery.

　　The blue curve is a lithium cobalt oxide battery, and the red curve is a lithium iron phosphate battery.

　　It can be seen from the figure that the OCV curve of lithium cobalt oxide has a certain slope, while the OCV curve of lithium iron phosphate is basically flat (don't consider the end diving).

　　In the SOC range of 5% to 90%, the open circuit voltage (OCV) of lithium iron phosphate batteries is basically concentrated between 3.2V and 3.3V.

　　Such a curve has a great influence on the discharge, mainly affecting the estimation accuracy of the SOC.

　　In electric vehicles, high-end energy storage, UPS and other fields, using lithium iron phosphate batteries, the key to accurate SOC calculation is high-performance chips and reasonable software design.

　　The specific method is that the chip collects current parameters, performs PID algorithms, uses software programs to calculate SOC, and then uses charging terminal parameters to perform SOC correction to achieve higher accuracy.

　　However, this method is difficult to be applied to common products that are very cost-sensitive. The main reason is that the cost is too high and the design is too difficult.

　　Lithium-ion battery (LIB) has become the main energy storage solution in modern social life. Among them, lithium iron phosphate batteries are a perfect replacement for lead-acid batteries, and they are the first choice for grid-connected peak shaving, off-grid energy storage, photovoltaic energy storage, UPS, data center and other industries.

　　At present, in the actual application of ordinary products, the SOC (power level) is still judged based on the battery voltage, resulting in very large errors and poor user experience.